Today's DC to DC switch mode power converters are typically required to provide insulation between the primary and secondary sides and to have high power density, high efficiency and low cost. In addition, many applications including uninterruptable power supplies (UPS), power supplies utilizing renewable energy sources (e.g. solar, wind, fuel cells), as well as aerospace power supplies require bi-directional (step-up and step-down) power conversion with isolated and regulated output. Examples of isolated and pulse width modulation (PWM) regulated bi-directional DC to DC converters are described in U.S. Pat. No. 5,140,509, U.S. Pat. No. 5,255,174, U.S. Pat. No. 7,433,207, U.S. Pat. No. 6,370,050 and U.S. Pat. No. 6,205,035. The pulse width modulation techniques control techniques employed in these converters typically feature so called “hard-switching” which can lead to significant switching losses and adversely impact the ability to achieve high power densities and high power conversion efficiencies.
Zero-voltage switching (ZVS) and zero-current switching (ZCS) are well established switching techniques for reducing switching losses which in turn allows for higher switching frequencies, reduced size of magnetic components, increased power density and reduced cost. U.S. Pat. No. 5,539,630, U.S. Pat. No. 6,370,050 and U.S. Pat. No. 6,330,170 describe bi-directional converters that feature ZVS but only in one of the directions of power conversion.
There is a need for an improved bi-directional DC to DC converter having a wide range of output voltage controllability in both directions of power transfer.
There is a need for an improved bi-directional DC to DC converter having a wide range of output voltage controllability in both directions of power transfer, the bi-directional DC to DC converter further providing galvanic isolation between the power source and the load.
There is a need for an improved bi-directional DC to DC converter having a wide range of output voltage controllability in both directions of power transfer, the bi-directional DC to DC converter employing the same components for power conversion in both directions of power transfer to reduce costs.
There is a need for series type, frequency controlled, bi-directional DC to DC resonant converter having a wide range output voltage controllability in both directions of power transfer, the resonant converter providing for loss-less switching operation in both directions of power transfer; loss-less switching operation within the whole range of load conditions (i.e. from no-load to full-load) and loss-less switching operation for all semiconductor devices in the circuitry.